It is current practice in orthopedic surgery to use plating systems for joining portions of a broken bone or for fusion of portions of separate bones. Such systems are composed essentially of plates and screws for aligning and holding the bone portions in a desired position relative to one another. Plating systems have usefulness in the spine, and have general skeletal use on the flat bones, such as the scapula and the pelvis, by way of example, and for use on tubular bones, such as the humerus, ulna, radius, femur, and tibia, by way of example.
Plates are usually provided to the surgeon for use in sets having a range of sizes so as to provide for such features as biological variability in size, the numbers of segments to be joined, and the length of the portions of bone to be joined. By way of example, a plating system for use on the anterior cervical spine may be used for joining from two to five vertebrae.
Problems associated with such plating systems have included, but are not limited to, an inability to gain adequate fixation and a failure to obtain solid bone healing where the plate will not allow the bone portions to come together over time. These occurrences may cause problems, be associated with surgical failure, and require further surgical procedures to repair the damage, remove the failed hardware, reattempt skeletal stabilization, and the like.
Although the plates may theoretically allow for proper alignment of the vertebrae and their rigid fixation, their use may be restricted by the types of screws available to the surgeon. Typical screws can only perform a single function, for example, lagging or locking. Lagging screws help to achieve anatomical correction whereas locking screws help to achieve more stable constructs. The head of a lagging screw is typically an external hex, and the lagging screw is used to lag two components (such as two bones or bone pieces, or a bone and a plate) together.
FIGS. 1A, 1B, 1C, and 1D depict the types of problems that may be encountered based on the screw limitations. FIG. 1A shows a graphic representing a fractured bone 2 or two separate bones 2 and a plate 50 extending across the broken or separated portion. In FIG. 1B, locking bone screws 4 are used and rotated or tightened using a rotation 8. The locking bone screws 4 provide for a rigid connection with the plate 50, but it is difficult to achieve anatomical reduction and restore functional anatomical relationships between the bones 2. As is evident, the locking bone screws 4 are insufficient to correct the relationship between the bones 2. In FIG. 1C, lagging bone screws 6 are used and rotated or tightened using a rotation 8. The lagging bone screws 6 provide for anatomical reduction and fixation to restore function anatomical relationships, but the lagging bone screws 6 do not provide stable fixation of the screws 6 to the plate 50. In other words, the fracture of the bone 2 does not receive adequate stability by rigid fixation or splintage to the plate 50. In order to combat this problem, the plate 50 typically requires some combination of both locking bone screws 4 and lagging bone screws 6. FIG. 1D depicts this situation where a lagging screw 6 is used to help reduce the fracture and achieve anatomical reduction, and locking screws 4 are used to provide fixed-angle stability. This solution adds complexity for the surgeon, however, in requiring different types of screws 4, 6 and not all of the screws 4, 6 lock and lag the plate 50 to the bone 2.
There remains a need, therefore, for an improved plating system. In particular, it would be beneficial to provide a single screw capable of locking each and every bone screw to the plate, and a single screw capable of lagging each and every bone screw to the bone.